A multilobe reflector antenna for RF sensing pointing of satellites

Abstract

The pointing accuracy of geostationary communication satellites is becoming increasingly important due to the more narrow communication beams. By improving the pointing accuracy, antenna design can be optimised for a smaller area, leading to better gain performance. Traditionally, IR sensors have been used to measure the pointing of the satellite. However, a more accurate way of providing data for the pointing of the large Ku and Ka band reflector antennas towards their coverage areas, is to measure the pointing angle of the satellite with respect to an RF signal from a ground station. Saab Ericsson Space has developed such an RF sensing system that works on the Ku band at 14 GHz. Each system works at a single frequency, but the design is such that it is easy to adapt the system for all frequencies between 14 and 14.5 GHz. The system consists of a small, lightweight (about 2.6 kg) reflector antenna with a reflector diameter of 0.4 m and a focal length of 0.25 m together with a sensing receiver. The measurement accuracy of the system when used on a geostationary communication satellite is about 0.01 degrees including constant, long term, daily and short-term errors. This paper deals mainly with the antenna that is included in the system. A description of the principle of operation is however also included.